1. Field of the Invention
This invention relates to an encapsulating composition and a light emitting device, more particularly to an encapsulating composition used in a light emitting device.
2. Description of the Related Art
Nowadays, light emitting diode (LED) technology focuses on improving illuminating efficiency, brightness, service life and reducing manufacturing cost. The illuminating efficiency of a LED light emitting device is mainly affected by a LED chip and an encapsulating composition used for encapsulating the LED chip. The conventional LED chip is made of gallium nitride (GaN, having a refractive index of 2.5) or gallium phosphide (GaP, having a refractive index of 3.45). The conventional encapsulating composition includes transparent resin (e.g., epoxy resin, silicone resin or urea resin) and has a refractive index ranging between 1.4 and 1.53. The difference between the refractive indices of the LED chip and the encapsulating composition results in only 30% of light extraction efficiency of the LED light emitting device although the LED chip may have 90% of light extraction efficiency. In order to enhance the refractive index of the encapsulating composition, organic and/or inorganic material is/are commonly added into the encapsulating composition.
Another conventional encapsulating composition is used in a white light emitting device and includes a transparent resin and a photoluminescent material (for example, phosphor particles). The photoluminescent material absorbs a portion of light emitted by the LED chip of the light emitting device and re-emits light with a different wavelength. The light emitted by the LED chip is mixed with the light re-emitted by the phosphor particles to obtain white light. However, the phosphor particles are relatively expensive since they are obtained from rare metal.
In yet another conventional encapsulating composition, in addition to the phosphor particles, light scattering particles are added into the transparent resin so as to increase collisions between light and the phosphor particles. The amount of the phosphor particles can thus be decreased. However, it is found that the brightness of the light emitting device would be decreased when the phosphor particles are partly replaced by the light scattering particles.